1. Field of the Invention
The invention generally relates to recording and/or reproducing apparatus for use with a flexible storage medium, such as a pliable magnetic disk, and, more particularly, to a double-sided recording device having magnetic heads disposed on opposite sides of the disk.
2. Description Relative to the Prior Art
U.S. Pat. No. 4,578,727 discloses a single-sided contact recording device that achieves a stable, constant interface between a moving disk and a magnetic head without the necessity of backing the disk with a pressure member. Such a stable interface is established by surrounding the transducing surface of the magnetic head with a small, flat air bearing surface. The head is supported in an opening in the air bearing surface to a negative pressure cavity. When the disk is rotated at relatively high speeds, a negative pressure is formed in the cavity that pulls a nearby section of the rotated disk into contact with the transducing surface of the head, thereby ensuring a constant interface for effective magnetic coupling. In companion U.S. Pat. No. 4,620,250, the air bearing surface is disposed at an angle with respect to the disk so that a leading edge of the air bearing surface penetrates slightly into the nominal plane of the rotating disk. This is believed to assist in the formation of strong coupling forces along the air bearing surface.
The air bearing surface has been further refined both as to shape and composition in U.S. patent application Ser. Nos. 19,468 and 136,793 (filed respectively on Feb. 26, 1987 and Dec. 22, 1987, and both assigned to the assignee of the present invention). The stabilizer described in the above patents is improved by establishing an abrupt transition in the leading edge of the air bearing surface that penetrates the nominal plane of the moving disk. The transition appears to act as a fulcrum, generating a force that turns a section of the moving disk about the transition and flattens the disk down upon the head. This force contributes to the coupling forces seen in the prior devices. The stabilizer is further improved if made from a ceramic material, such as barium titanate. A stabilizer of such material is operative for long periods with relatively low frictional drag between the disk and the air bearing surface, a condition that lowers current draw upon the disk drive motor. To date, such stabilizer devices as described in these patents and applications have not been disclosed for use in double-sided recording applications.
Double-sided recording on a floppy disk has been used to increase capacity and facilitate data transfer operations. As with most single-sided recording, pressure is required on the opposing side to urge the disk against the head. A typical double-sided contact system is disclosed by U.S. Pat. No. 4,151,573, which shows a fixed head on one side of a disk and a cantilevered, gimbal-mounted, movable head on the other side. In operation, the disk is confined against the fixed head, despite perturbations in movement of the disk, by the pressure of the movable head. Typically, the disk is contained within a protective plastic jacket. A shutter on the jacket is moved aside to reveal a windowed opening through which the heads can contact the disk. For double-sided recording, inasmuch as the window is quite small, the heads are ordinarily in direct opposition or slightly offset in a radial direction to avoid flux interaction. This arrangement is desirable in any case because the disk, according to the prior art, is urged against one head by the force of the other--as further illustrated by U.S. Pat. No. 4,320,426, in which the disk is conformed to a wavy contour where it is captured between two radially offset heads. Such teaching, however, does not encourage the successful juxtaposition of a pair of un-backed air bearing surfaces (as described in U.S. Pat. Nos. 4,578,727 and 4,620,250) because the opposed surfaces are intolerant of such close interaction.